1. Field of the Invention
The present invention relates to control of a compressor in a gas turbine engine and, more particularly, to control of a compressor by detecting and compensating for aerodynamic instabilities.
2. Description of the Related Art
With the introduction of the gas turbine engine, the speed and reliability of air travel has improved significantly. The gas turbine engine also known as a turbojet engine provides propulsion through the acceleration of a stream of air or gas which is expelled at a high velocity. The typical turbo-jet engine includes three basic functional elements a compressor for gathering and pressurizing the air, a combustor chamber for heating the already pressurized air and a turbine for translating the energy released from the pressurized and heated air into mechanical energy and thrust to propel the aircraft forward. While jet engine technology has advanced one of the safest and fastest growing markets for mass transportation, the technology still suffers from problems caused by rotational stall and surge caused by changes in the air flow rates through the compressor. Such problems can be magnified by environments where the speed of the engine and the air speed in which the engine operates are changed. While providing an optimum operating environment can reduce the occurrence of stall and surge, these same problems have arisen in gas turbine engines implemented in the power generation field where the engine are operated at generally constant speeds with a controlled air flow environment.
The problem is that stall and surge are more likely to occur when the engine is operated at or near its optimum operating speed. One solution to the stall and surge problem has been to implement a feedback and control system that uses measured pressure or pressure and temperature characteristics to detect when conditions relating to stall and surge are about to occur. The measured signals are processed by a control circuit that detects a stall or surge condition and adjust the engine operating parameters to eliminate the measured conditions indicative of a stall or surge in the engine. While such solutions have worked well in implementations relating to turbine engines relating to power systems, such solutions have been hampered in the use of such solutions for jet engines. One problem has been the installation of sensors to detect the air flow conditions. The operational environment of the turbine engine causes the sensors to be subjected to extreme temperatures and vibrational conditions. While the sensors in gas turbines for power generation and the like may be mounted in a way to isolate the sensor from such harsh conditions, the turbine engines used in jet aircraft have weight and aerodynamic considerations that make such techniques impractical. Compounding the problems in turbine engines for jet aircraft has been the advances made in the introduction of aluminum and composite materials into the jet engine design. Such materials help to incrementally increase efficiency and reduce weight; however, such materials have also increased vibration encountered in the engine. The result of these advances is the operating conditions in which the sensors must operate have become more severe.
Thus a need exists for a way to implement a surge detection system in a jet aircraft which improves the operational parameters of the engine without sacrificing the aero dynamic and weight considerations in the design.